Sources briefed on the matter said third-party agents have made contact with the hostage-takers, who have not been publicly identified, and talks to free the men are under way.

The U.S. government is not considering any type of military operation to rescue the seamen, officials said. The kidnapped men, employees of the maritime transportation company Edison Chouest Offshore, have only been identified as the Captain and Chief Engineer of the C-Retriever, an oil supply vessel. The U.S. government itself has a longstanding policy against complying with ransom demands, but private companies are not subject to such a policy.

The FBI is assisting in the matter but is not negotiating directly with the kidnappers, sources said. Spokesmen for the FBI have declined repeated requests for comment, saying they do not want to jeopardize the safety of the captives.

The C-Retriever was attacked in the early daylight hours Oct. 23 by an unknown number of armed assailants who then separated the crew by nationality and made off with the Americans, a Pentagon official told ABC News the day of the attack.

In the days since, a proof-of-life call was made and the U.S. government has verified that the two Americans are being held on land as their fate is negotiated.

While globally piracy was down last year to its lowest levels in seven years, cases in Nigeria are on the rise. According to the International Maritime Bureau, pirate attacks off Nigeria's coast have jumped by a third this year -- allegedly perpetrated by criminal gangs who are looking for cargo ships with commodities, and seeking ransom for hostages. Around the world there have already been more than 200 "incidents" involving piracy this year, including 11 hijackings, the IMB said.

In 2009, on the other side of Africa, American Capt. Richard Phillips was held hostage on the Indian Ocean by a group of Somali pirates for five days before he was freed in a daring rescue by U.S. Navy SEALs. Hollywood recreated that ordeal in a recent blockbuster film starring Tom Hanks as Capt. Phillips.

Phillips, who returned to shipping just over a year after his ordeal, recently told ABC News that these days dangers from pirates is part of life for a captain.

"If you don't want to deal with piracy, you need to get another job," he said before the most recent incident.